well if you need to cut a few lbs for a photo shoot or competition, then go for it. if you wanna lose fat, its a waste of time

I do not have a study for this but I have tried to cut for photos dropping the last bit of water via sauna and in my case it made me look really flat so I would not do this. Now in my MMA and wrestling days we cut water to make weight this way.

OP if you enjoy sitting in the sauna then do it once in a while, I myself find it relaxing after a workout so I tend to do that on a rough leg day or what ever.

It's nice to sit and then take a nice cool shower but it's not going to cause fat loss and any water weight SHOULD be replenished afterwards unless you're cutting weight for a goal. Therapeutic? Maybe. Fat loss aide? No

Def feel its more therapeutic and to validate whats already been said only water displacement ,but def put the water back on later. For valid fat loss Id imagine the increased temp would become harmful sooner than valid fat loss could be observed. Curious to see if there is a study out on it tho. Hope my 2 cents helps